The Efficiency Rule

Stay the CourseHappy New Year! ‘Tis the season for a new resolve to do things better. For many of us, a better 2019 begins with doing more. But for those with limited time and energy, there’s only so much ‘more’ we can do. Instead, we endeavor to do what we are already doing better.

To run better without running more is to be efficient. Given the limitations of time and energy, efficiency is the gold standard for both improvement and peak performance, especially for those of us who are already running pretty far and fast. Efficiency is king.

[Author’s Note: In technical scientific terms, ‘efficiency’ refers to the percent of expended energy that is used for doing work (as opposed to energy lost as heat). Speed or distance per unit of energy is referred to as ‘economy.’ However, because economy has a financial connotation for many people, we use the term efficiency instead.]

What if you cannot run very frequently, far, or fast? Then injury has probably derailed your running. Given that a full three-fourths of all runners will incur some sort of injury each year, the odds are strong that most of us have been recently tripped up and slowed down by an ache or pain.

What if fast and healthy running were truly linked? Beyond the benefits of consistent running, what if top speed and injury prevention were two sides of the same coin? In fact, this is the essence of efficiency: minimal body stress and maximal propulsion.

The Frustrations and Failures of Running Research

What does the research say about this? To begin, it’s been a long and convoluted road. Academic researchers have finally caught on to the notion of stride efficiency in running injury. Biomechanists and orthopedic clinicians have been studying running injury for decades. However, that injury incidence hasn’t budged from a supermajority of runners each year is disappointing (if not embarrassing) for medical professionals, coaches, and runners. ‘Evidence-based’ interventions of a certain strength routine or a miracle stretch have hardly scratched the surface of our collective injury epidemic. After years of repetitive failure, researchers are beginning to put down the resistance bands and stretch routines, and instead examine how we run.

But if research has let us down for this long, who is to say that research-based running-mechanics guidelines will be any different? Perhaps the answer lies in how to interpret and apply that research in the real world.

Correlation Versus Coaching: Applying Injury Research to Your Running

Most quantitative research is based the relationship–a correlation–between two measures:

  • Some measurable aspect of a runner. Examples include range of motion, strength, or a quality of movement (heel strike versus forefoot landing).
  • An outcome measure. Examples are the incidence and duration of pain and injury.

For example, research has shown that hip-abductor and external-rotator muscle weakness are correlated with lower-extremity injury. Importantly though, such associations do not imply causation. It’s still possible to have weak hips and be healthy, just as it’s possible to have strong hips and get injured. However, correlations are often all we have to go by in establishing root causes.

Now what? Research has connected these two dots:

  • Weak hips
  • Injury

For academics, the next logical question is, how do we make the hips stronger? Back to the research, where we endeavor to find the most effective strength exercises. The best exercises to activate and strengthen hip muscles, as determined by laboratory studies, are then recommended.

Therefore, if weak hips correlate with injury and exercise routine #1 creates the strongest hips, then exercise routine #1 must prevent injury. Right? Not really. It doesn’t work, and we all know it because we’ve tried it.

Evidence-based recommendations are based–and lean too heavily–upon correlations. It may correlate with weakness, but running injury is the result of a complex and often messy amalgam of factors. It’s a major stretch to ascribe injury to a single variable. It’s an even bigger stretch to believe that performing an isolated strength or mobility exercise will completely rectify a complex injury pattern. That is why your clam-shell routine never really cures that knee injury, no matter how many sets you do a day or the thickness of your stretch band (and backside muscle).

Researchers have caught on, and now they’re finally studying stride mechanics. Great! But hold on. Before you get too excited, let’s see about our old problem, correlation. The most promising body of running-stride research today is on stride cadence. This variable looks at how many steps per minute we take when running. This correlates with running injury because the slower the running cadence, the longer we spend on the ground, and the greater the energy absorbed by our legs. Today, both cadence and ground-reaction (landing) forces are easily measured on high-tech treadmills. As such, numerous studies have demonstrated that slow cadence causes increased ground-reaction forces and increased ground-reaction force correlates with injury. Thus, faster cadence must prevent injury.

Trusting that correlation, how do we best increase cadence? Unfortunately there is no clear consensus, other than ‘move your feet faster,’ which seems dubious. Current research recommends running with a metronome (or listening to songs with a 180-beats-per-minute tempo–the evidence-based correlate for efficient cadence), but there is no specific strategy for how to more quickly strike the ground. Nor is there any discussion on how ‘faster feet’ might affect the rest of the stride. Anyone else skeptical? Something’s missing.

Efficiency is Peak Performance and Minimal Strain

It may be time to cast aside the medical-research hat and put on the athlete/coach cap and think about efficient running. If efficiency is the greatest speed or distance per unit of energy, then efficiency also implies minimal wasted energy. Injury is most strongly correlated with high landing forces or energy that is bashed into the ground (and the legs) rather than used for propulsion.

Thus, efficiency is now a compelling argument for both injury relief and prevention, as well as peak performance. Efficient running is the fastest and lowest-stress running. Now we have a worthy metric.

The Efficiency Rule Defined

Based on the theoretical connection of minimal strain and maximal speed, I put forth the ‘Efficiency Rule,’ which is defined as: “Any running-stride adjustment that sustainably relieves pain must also make you faster.” To be clear, relieving pain means decreasing stress, strain, or another objective force measure.

The Efficiency Rule implies that in order to create a running injury there is an efficiency drain, a place where energy intended for propulsion is being absorbed excessively by the body. Thus, by virtue of the law of conservation of energy, decreasing body stress increases the amount of available energy for propulsion. This means we have a new standard for any running-stride optimization: efficient, low-stress running will result in faster running.

Efficiency: Sustainability and Performance and why Barefoot Running Failed (Most of) Us

Within this definition are the two key operators of sustainability and performance. Both must be satisfied in order for a running intervention to qualify under the Efficiency Rule.

Performance relates to measures of velocity. Either our top speed or our overall endurance at relatively high speeds will improve with a strain-reducing running strategy. We will discuss this in more detail below.

Sustainable interventions:

  • Make pain go away and keep it away; and
  • Must not create a different strain or injury (in the longer term).

Every intervention has second-order effects, which are side effects that emerge as a result of the adjustment. In the case of cadence adjustment, what second-order effects could possibly arise from simply ‘moving your feet faster?’ (Spoiler alert: many.)

Likewise, the demise of the minimalist-footwear boom of the mid 2000s is an example of both the limitations of correlation as well as unseen second-order effects. Indeed, runners do land ‘softer’ in more minimal shoes. (And, as we’re finding out, the converse is also true.) But rather than automatically adopt an efficient (‘fast’) stride, what most minimalist runners did was shift that strain from bone and joints to soft tissues, thereby overloading the calf and lower-leg muscles. This caused a strong second-order effect of increased muscle injury that turned many away from minimal shoes. Thus, arbitrary stride changes are seldom enough to create long-lasting improvements in injury prevention.

I used to joke that you could cure a foot injury if you ran on your hands and knees. Indeed, simply changing the load on the foot will allow it to heal, right? But does this satisfy the Efficiency Rule? Let’s see:

  • Sustainability. Is running on the hands and knees sustainable? What are the second-order effects?
  • Performance. What is one’s peak velocity and endurance while hands-and-knees running?

This may seem silly and irreverent, but here’s a real, stranger-than-fiction example. A recent study demonstrated that significantly less landing forces were incurred in the legs… if you didn’t run. That is not a typo. Performing “grounded running”–a style of movement akin to speed walking where one foot is always on the ground–is significantly less stressful than “aerial running,” also known as… running!

This is a classic example of an intervention that blatantly fails the Efficiency Rule:

  • Sustainability. Will speed-walk-running sustainably relieve pain and prevent injury? Probably (especially for lower-leg, ankle, and foot pain).
  • Performance. Will speed-walk-running make you a faster runner? Absolutely not. The float phase is crucial for both top overall speed and sustained top endurance speed. (This is not to say this isn’t a useful technique, but the majority of runners want to run, are capable of running through the air, and wish to continue doing so.)

The same goes with cadence training. Simply moving your feet faster is a strategy that does not satisfy the Efficiency Rule:

  • Sustainability. Faster cadence may decrease ground-reaction forces, but second-order effects may include decreased hip mobility (which can increase hip and hamstring strain), among others.
  • Performance. Moving your feet faster at the expense of hip mobility (and without optimizing other variables) will, over time, decrease both top speed and endurance.

Thus, the bar has been raised on how to relieve pain. It’s not good enough to simply move differently. We must move better.

The Sight and Speed Test: Look Fast and Be Faster to Run Efficiently

If the Efficiency Rule mandates faster running from whatever stride adjustment we make, the easiest way to assess fast running is by visual inspection. This is the essence of coaching. Across all sports, there is a fairly narrow standard of ideal technique for any given movement (individual quirks notwithstanding). Skilled coaches know efficient movement and they know their sport-specific standards very well.

As such, the standard for any new running-stride technique is simple. Does it look good? Do you look like a ‘good, fast runner’ doing that new thing? When it comes to posture, pawback, and arm swing, you probably do! (But for speed walking, hyper-cadence shuffling, or bear crawling? Probably not!)

How it feels and how difficult it is, is initially irrelevant. Anything new feels and is initially more difficult due to neuromuscular novelty. This is typical of new learning. With repetition, both the feel and ease greatly improve. But in the short term, if it looks good, you’ve nailed the first step. This is why, as a coach-clinician, I always employ a video tablet to record and immediately provide visual feedback to my clients. (Real-time feedback is most ideal.)

The second metric is speed. Does your stride adjustment make you faster? Like visual appearance, speed improvement is usually immediate. Optimal alignment, leg motion, and arm movements will result in immediate improvement in both top-end speed and endurance. That said, you may not have the intrinsic strength and endurance to maintain it for very long, but like fitness, that new stride ability will develop with repetition (and specific exercises and drills).

Summary

Injury and performance are tightly intertwined. Energy that creates injury is energy robbed from performance, and energy preserved from the legs is used to propel. The Efficiency Rule is the litmus test for any injury-prevention strategy because it aims to redirect energy from strain to speed, from frustration to the finish line–fast!

It’s not only logical but enormously hopeful. For me, it’s both exciting and deeply rewarding to help a runner not only overcome and prevent injury, but to also get faster at the same time. Each of us runners should be equally hopeful and shoot for the Efficiency Rule standard. We should endeavor to make an adjustment that not only gets and keeps us healthy, but also makes us faster. Such a double-barrel effect is something worthy of our resolve!

Call for Comments (from Meghan)

  • Have you ever intentionally or unintentionally changed an element of your running stride that made your running both feel better and become faster?
  • Alternately, have stride changes ever resulted in unintended, negative side effects?
Joe Uhan

is a physical therapist, coach, and ultrarunner in Eugene, Oregon. He is a Minnesota native and has been a competitive runner for over 20 years. He has a Master's Degree in Kinesiology, a Doctorate in Physical Therapy, and is a USATF Level II Certified Coach. Joe ran his first ultra at Autumn Leaves 50 Mile in October 2010, was 4th place at the 2015 USATF 100K Trail Championships (and 3rd in 2012), second at the 2014 Waldo 100K, and finished M9 at the 2012 Western States 100. Joe owns and operates Uhan Performance Physiotherapy in Eugene, Oregon, and offers online coaching and running analysis at uhanperformance.com.